This invention relates to improved optical dimension gauging instruments now commonly referred to as laser micrometers.
Examples of optical or laser micrometers are shown in the following U.S. Pat. Nos. : 2,812,685, 3,856,411 3,765,774, 3,856,412, 3,592,545, 3,686,437, 3,743,428, 3,870,890, 3,853,406, 3,905,705.
Laser micrometers are effective in measuring certain products by non-contact methods, and the resulting measurement signal may be used to control the process by which that product is manufactured. The accuracy and tolerance to which the end product can be made depends upon whether the laser micrometer can see the article and the nature of the disturbing influences which are present.
In certain maufacturing processes, the atmosphere surrounding the object being measured may be hostile due to dust or vapor, and in those processes where the measurement must be inside of a closed container, dirt, dust, water and other foreign objects may collect on the viewing windows.
For example, in the manufacture of insulated wires wherein material extruded on the wire is vulcanized in what is known as the continuous vulcanization process, the coated wire is enclosed in a steam tube hundreds of feet long. Attempts have been made to measure the hot diameter of the wire while in the steam tube using conventional laser micrometers positioned on either side of sight glass windows. Such attempts have only met with partial success because of the variable and optically hostile atmosphere within the tube, water droplets on the wire, in the air and on the sight glass, and occasional momentary irregularities resulting from the extruding process prevent accurate continuous diameter measurements.
Another example is in the manufacture of precision steel tubing where it is important to have an accurate measurement of the hot outside diameter of the tubing after it passes through rollers which control its dimensions. Since the tubing is frequently red hot at the desired point of measurement, a non-contacting type gauge is normally used, such as a laser micrometer. However, the optical atmosphere in a steel mill is generally poor, especially since the hot tubing is frequently surrounded by vapor, dust and dirt.